The human being in the normal condition, that is, in good health, has a constant intracranial cavity volume peculiar to himself. However, if he suffers from, for example, a lesion such as cerebral tumor, hematoma or the like or any other intracranial disease, the volume of the intracranial cavity is increased. It is said that when the increase reaches about 10% of the normal cavity volume, the intracranial pressure rises and leads to a sthenia of the intracranial pressure, whereby a variety of diseases will be caused. To make clear what these diseases and determine appropriate therapy for them, it is necessary to throw a pathologic light on the sthenia of intracranial pressure. The means and methods for such elucidation have been studied in various fields of medicine, but no satisfactory means and methods have yet been proposed. However, one of the most important means for the elucidation is the measurement of any change of the intracranial pressure (intracranial pressure waveform). Heretofore, various many methods of re the intracranial pressure have been studied and tried. Such conventional methods include, for example, the latex balloon method in which a latex balloon charged with water is introduced above the dura mater or into the cerebral ventricle inside the cranium to measure the water pressure in the balloon, thereby measuring the intracranial pressure and its waveform, and the EDP measuring method in which a part of the cranium is opened to make an osseous window through which the dura mater is exposed, a strain gauge is put into contact with the dura mater and a change of the intracranial pressure is measured as a change of strain measured by a dynamic strain gauge connected to the strain gauge. However, since the measurement of the intracranial pressure by these methods is done with an invasion to the cranium, the patient must be subject to a craniotomy and have a sensor placed inside the cranium. Thus, the conventional methods for intracranial pressure measurement have problems since the patient must bear a heavy physical and socioeconomic burdens because he has the possibility of being infected and must be in rest as hospitalized to maintain his health. In addition to the above-mentioned methods, there has been proposed a telemetry system, as a noninvasive and safe method, in which an electric resonant circuit composed of an inductance and capacitance is used of which the resonant frequency is changed by changing one of the values, inductance or capacitance, with the dislocation of a bellows or diaphragm due to the intracranial pressure and measured from above the scalp. However, this method also have practical problems; since air is used as compression medium, it, if any between the scalp and cranium, is easily affected by the temperature, the measuring gradation is required for each patient and the measuring accuracy is also far from the practical use. Heretofore, there has not yet been provided any apparatus capable of measuring the intracranial pressure easily, noninvasively without any malinfluence on the brain inside and with a high reliability, and those in the clinical fields have long waited for such apparatus.
As having been described in the foregoing, the conventional measurement of intracranial pressure has been done by the methods with an invasion to the cranium in almost all the cases while being one of the most important means in the elucidation and therapy of the intracranial pressure sthenia. There have not yet been proposed any method and apparatus which satisfy the required safety and reliability for the measurement and can make the measurement with a reduced socioeconomic burden to the patient. On the other hand, the apparatus by the noninvasive method is just under study and development, and the accuracy and costs thereof are not yet at the practical stage.
The present invention has an object to overcome the above-mentioned drawbacks of the conventional techniques by providing an apparatus capable of measuring and recording the intracranial pressure waveform from outside the cranium easily, safely, noninvasively, highly reliably and without any malinfluence on the brain inside.